This invention relates generally to protection circuitry, and more particularly to a method and system for inserting an un-powered circuit into a powered-on (hot) running system.
As chip capacity continues to significantly increase, the use of programmable gate arrays (PGAs), is particularly field programmable gate arrays (FPGAs), is quickly replacing the use of application specific integrated circuits (ASICs). An ASIC is a specialized chip that is designed for a particular application. Notably, an FPGA is a programmable logic device (PLD) that has an extremely high density of electronic gates as compared to an ASIC. This high gate density has contributed immensely to the popularity and flexibility of FPGAs. Furthermore, it has become a common industry practice to xe2x80x9cHot-swapxe2x80x9d plug-in boards that contain integrated circuits such as FPGAs into powered-on systems.
Hot-swapping or hot insertion is a potentially dangerous method of inserting an un-powered board (containing integrated circuitry) into a power-on running system. Typically, concerns revolve around avoiding physical harm or permanent damage to the system or to the inserted board and avoiding data corruption or any transient system upsets.
Plug-in boards or printed circuit boards (PCB) typically need replacement in a system due to system failure, routine maintenance, or system upgrading. There are basically two ways of plugging in a PCB which contains a number of integrated circuit devices into a main system or a system backplane. One is to power down the whole system, plug in the board and then power up the system again. This method fails to meet the reality and practicality of today""s market demands requiring hot-swaps. The alternative is to plug in the boards or PCBs without powering down the system at the risk of damaging either the system or the boards being plugged in or both. There could be various reasons for the preference for hot swapping. For example, it may take too long for the system to be rebooted or the system performance could not be interrupted during repair work.
The problem that arises from hot swapping is the relatively long time it takes for the power to reach operating levels on the board due to the heavy capacitive load. Since the parts on the board are being connected to an active system, the input/output (I/O) pins of the integrated circuits on the board may see a logic level 1 (3.3 v or 2.5 v for example) long before the power is restored to the chip on the board. When this happens, due to the forward biasing of a pn junction diode at a pad of the board and due to the backward conduction of a pull-up driver at the pad, a high amount of current will flow through the package which may damage the system. Thus, a need exists to circumvent the problem described above when plugging in an integrated circuit microchip or a system board containing microchips into a powered-up system.
In a first aspect of the present invention, a hot swap protection circuit for an integrated circuit being plugged into a powered-up system comprises a first circuit for detecting a hot swap condition, a second circuit coupled to the first circuit for preventing a pn junction diode in a pull-up transistor from going into a forward bias condition, and a third circuit coupled to the first and second circuits for preventing the pull-up transistor from turning on during the hot swap condition.
In another aspect of the invention, a method of protecting a powered-up system during the insertion of an integrated circuit comprises the steps of detecting a hot swap condition, preventing a forward bias condition in a pn junction diode of a pull-up transistor of the integrated circuit during the hot swap condition, and biasing the pull-up transistor coupled to a pad of the integrated circuit to remain turned off during the hot swap condition.
In yet another aspect of the present invention, a method of protecting a powered-up system during the insertion of a printed circuit board containing an integrated circuit, comprises the steps of detecting a hot swap condition, isolating an nwell of a pmos pull-up transistor from a power source of the powered-up system during the hot swap condition, and preventing the pmos pull-up transistor coupled to a pad of the printed circuit board from turning on during the hot swap condition.